Immobilization and aqueous durability of Nd2O3 and CeO2 incorporation into rutile TiO2

Synroc is recognized as the second generation waste form for safety disposal of high-level radioactive waste (HLW). In this study, the Synroc mineral of rutile was employed as host phase for the immobilization of Nd2O3 and CeO2, which were selected as surrogates of trivalent and tetravalent actinide nuclides. Rutile waste forms with different Nd2O3 and CeO2 incorporations were prepared under normal pressure sintering. Nd2Ti2O7 pyrochlore was produced as the target phase in 1100 °C calcined Nd-bearing TiO2. Lattice stabilization of CeO2 in rutile TiO2 could not be accomplished even under 1500 °C sintering. The 28 day normalized leaching rates (LRi) of Ti and Nd in Nd-bearing rutile, which decline congruously as the Nd2O3 content increases, are lower than 3×10−5 g m−2 d−1. The incorporation of CeO2 significantly impairs the aqueous durability of rutile waste form.